1. Field of the Invention
The invention relates to a write signal generator in an optical disk drive, and more particularly to an aligned write signal generator with delay calibration in an optical disk drive utilizing an alignment unit to align the write signals with each other in time.
2. Description of the Related Art
FIG. 1 illustrates a block diagram of a laser power control system in a conventional optical disk drive. Referring to FIG. 1, the laser power control system 10 includes an EFM (Eight-to-Fourteen Modulation) encoder 11, a write signal generator 12, a LD driver (Laser diode driver) 13, and a LD (Laser Diode) 14. The EFM encoder 11 receives the input data and generates the EFM signal according to the EFM encoding rule. The write signal generator 12 receives the EFM signal and converts the EFM signal into a plurality of write signals, e.g. three write signals WS1, WS2, WS3 as shown in FIG. 1, according to the write strategy waveform generating rule. The write signal generator 12 typically includes a write strategy pulse generator 121, a flip-flop unit 122, and a write signal calculator 123. The LD driver 13 receives the plurality of write signals and integrates them into a drive signal to drive the LD 14. How the write signal generator 12 converts the EFM signal into a plurality of write signals according to the write strategy waveform generating rule is a well-known art in this filed and can be found in U.S. Pat. No. 6,445,661, so detailed descriptions thereof will be omitted.
Along with increase in write speed of the optical disk drive, the timing accuracy among the write signals becomes more critical. Correspondingly, the problems of the waveform deformation caused by the digital logic gate, buffer, and output driver within the write signal generator also become more serious owing to, for example, the different delay time among the write signals. FIG. 2 shows the ideal waveforms of three write signals and the corresponding drive signal, wherein FIG. 2A shows three write signals generated by an ideal write signal generator, and FIG. 2B shows the drive signal generated by the LD driver. Because the three write signals WS1, WS2 and WS3 are not deformed, the drive signal generated by the LD driver is consequently quite ideal.
FIG. 3 shows the deformed write signals and the corresponding drive signal, wherein FIG. 3A shows three write signals generated by the write signal generator 12, and FIG. 3B shows the drive signal generated by the LD driver. As shown in FIG. 3, because the three write signals WS1, WS2 and WS3 are not aligned in phase (or say, not aligned in time), the drive signal generated by the LD driver is seriously deformed. If the optical disk drive outputs such a deformed drive signal to the LD 14, the data may not be recorded in the optical disk in a proper format, thereby causing data error when one tries to reproduce the data in the optical disk. Therefore, it is an important subject to provide phase adjusted write signals.